Heretofore, in various types of radio equipment or in other communication equipment, couplers using hybrid circuits (hereafter referred as "hybrid coupler") have been used.
A hybrid coupler is a circuit having three or more ports (input/output terminals) and used as a power divider or combiner, or as a phase shifter. The conventional hybrid coupler will be described with reference to the accompanying drawings.
FIGS. 9 to 16 are diagrams used for explaining the prior art. In which, FIG. 9 shows the block constitution of a typical hybrid coupler, FIG. 10 shows a circuit example of a typical capacitive coupling type hybrid coupler, FIG. 11 shows a circuit example of a typical inductive coupling type hybrid coupler, FIG. 12 shows an example of the prior-art hybrid coupler practically mounted on a wiring board, FIG. 13 shows phase shift characteristics of the prior-art inductive coupling type hybrid coupler, FIG. 14 shows band pass characteristics the prior-art inductive coupling type hybrid coupler, FIG. 15 shows phase shift characteristics of the prior-art capacitive coupling type hybrid coupler, and FIG. 16 shows band pass characteristics of the prior-art capacitive coupling type hybrid coupler.
In these FIGS. 9 to 16, C1 to C6 and C11 to C14 denote capacitors, L1, L2 and L11 to L14 denote inductors, P1 to P3 denote ports (input/output terminals), HY denotes a hybrid circuit, Re denotes a resistor, and Pt denotes a wiring board (printed wiring board).
As shown in FIG. 9, the typical hybrid coupler is formed by a hybrid circuit HY with three ports P1 to P3 and a resistor Re connected to its terminal not used as a port. In the hybrid coupler of this figure, when a signal is applied to the port P1, this signal will appear both at the port P2 and the port (when the coupler is used as a power divider). When a signal is applied to the port P2, however, the signal will appear at the port P1 but will not appear at the port 3 due to the isolation between the ports 2 and 3. Also, when a signal applied to the port P3, it will appear at the port P1 but will not appear at the port P2. Furthermore, when signals are simultaneously applied to the ports P2 and P3, those signals will be combined so as to appear at the port P1 (when the coupler is used as a power combiner).
FIGS. 10 and 11 show examples of the hybrid coupler as 90.degree. phase shifters by configuring their circuits so that when a signal is applied to the port P1, signals having phase difference of 90.degree. with each other will appear at the ports P2 and P3, respectively. FIG. 10 is a circuit example of a capacitive coupling type hybrid coupler formed by the hybrid circuit HY with capacitors C1 to C6 and inductors L1 and L2, whereas FIG. 11 is a circuit example of an inductive hybrid coupler formed by the hybrid circuit HY with capacitors C11 to C14 and inductors L11 to L14.
In these examples of FIGS. 10 and 11, if the inductance values of the inductors L1, L2 and L11 to L14 are respectively expressed by the same references L1, L2 and L11 to L14 and the capacitance (static capacitance) values of the capacitors C1 to C6 and C11 to C14 by the same references C1 to C6 and C11 to C14, the inductance and capacitance values of the inductors and the capacitors are set as, L1=L2, C2=C5, C1=C3=C4=C6, L11=L12, L13=L14 and C11=C12=C13=C14.
FIG. 12 shows, as an example of practical mounting of the above-mentioned hybrid coupler on a wiring board, a capacitive coupling type hybrid coupler with a circuit configuration shown in FIG. 10. In this example, the inductors L1 and L2, the capacitors C1 to C6, and the resistor Re are provided as discrete parts and mounted on a printed wiring board Pt.
Meanwhile, in such the capacitive coupling type hybrid coupler with a circuit configuration shown in FIG. 12, when a signal is applied to the port P1 and signals shifted by 90.degree. are derived from the ports P2 and P3, an error .epsilon..sub.p in the phase difference will depend on the following value .DELTA..
If the inductance values of the inductors L1 and L2 are expressed by L1 and L2 and the capacitance values of the capacitors C1 to C6 by C1 to C6, the .DELTA. is given as .DELTA.=L1/L2, .DELTA.=C1/C3, .DELTA.=C2/C5, .DELTA.=C6/C4. If .DELTA.=1, .epsilon..sub.p =0, and if .DELTA.&gt;1 or .DELTA.&lt;1, .epsilon..sub.p =E (error exists).
On the other hand, in the inductive coupling type hybrid coupler with a circuit configuration shown in FIG. 11, the error .epsilon..sub.p of the phase difference in the signals obtained from the ports P2 and P3 will depend on the following value .DELTA..
Also in this case, if the inductance values of the inductors L11 to L14 are expressed by L11 to L14 and the capacitance values of the capacitors C11 to C14 by C11 to C14, the .DELTA. is given as .DELTA.=L13/L14, .DELTA.=L11/L12, .DELTA.=C11/C12, .DELTA.=C13/C14. If .DELTA.=1, .epsilon..sub.p =0, and if .DELTA.&gt;1 or .DELTA.&lt;1, .epsilon..sub.p =E (error exists).
Therefore, if the hybrid coupler is formed by the hybrid circuit HY with discrete components as shown in FIG. 12, since there are variations among capacitances and inductances of the individual components, the value of .DELTA. may sometimes deviate from .DELTA.=1 when the hybrid coupler is mass-produced. For this reason, it has been necessary to make adjustments by changing the components, for example.
With reference to FIGS. 13 to 16, description will be made of examples of the phase shift characteristics and the band pass characteristics (characteristics as a 90.degree. phase shifter) of the inductive coupling type hybrid coupler and the capacitive coupling type hybrid coupler mentioned above.
In these FIGS. 13 to 16, the abscissa represents the frequency f (MHz), and in FIGS. 13 and 15, the ordinates represents the phase difference .phi., while in FIGS. 14 and 16, the ordinates represents the output ratio (dB).